Cytochrome P450 enzymes are a heme-containing family that play central roles in oxidative, peroxidative and reductive metabolism of numerous endogenous and exogenous compounds, including many pharmaceutical agents. Substances known to be metabolized by P450 enzymes include steroids, bile acids, fatty acids, prostaglandins, leukotrienes, biogenic amines, retinoids, lipid hydroperoxides, phytoalexins, pharmaceuticals, environmental chemicals and pollutants. P450 substrates also include natural plant products involved in flavor, odor, flower color, and the response to wounding. P450 enzymes and other drug-metabolizing enzymes maintain steady-state levels of endogenous ligands involved in ligand-modulated transcription of genes effecting growth, apoptosis, differentiation, cellular homeostasis, and neuroendocrine functions. The metabolism of foreign chemicals by P450 enzymes can produce toxic metabolites, some of which have been implicated as agents responsible for birth defects and tumor initiation and progression.
The P450 gene superfamily is likely to have evolved from an ancestral gene present before the prokaryote/eukaryotedivergence. The number of individual P450 genes in any mammalian species is estimated at 60 to 200. The CYP2C and CYP3A subfamilies are unique in that they are present in large amounts in human liver microsomes, and there are many forms in each subfamily. Several human cDNAs encoding CYP3A proteins have been identified. The most important of these are CYP3A4, CYP3A5 and CYP3A7. CYP3A4 and CYP3A7 genes are 87% homologous by amino acid and 95% homologous by nucleotide sequence, while CYP3A4 and CYP3A5 are only 88% homologous in the coding region. CYP3A4 and CYP3A7 are 91% homologous in the 5xe2x80x2-flanking sequences, differing by the presence of a unique P450NF specific element (NFSE) and a P450HFLa specific element (HFLaSE), respectively (Hashimoto et al, 1993).
It has been shown that polymorphisms in the CYP2D6 gene correlates with enzyme activity measured by phenotyping with dextromethorphan or debrisoquine (Sachse et al. (1997) Am. J. Hum. Genet. 60:248-295).
The CYP3A subclass catalyzes a remarkable number of oxidation reactions of clinically important drugs such as quinidine, warfarin, erythromycin, cyclosporin A, midazolam, lidocain, nifedipine, and dapsone. Current estimates are that more than 60% of clinically used drugs are metabolized by the CYP3A4 enzyme, including such major drug classes as calcium channel blockers, immunosuppressors, macrolide antibiotics and anticancer drugs, see Brian et al. (1990) Biochemistry 29:11280-11292.
Expression profiles for each member of this family varies significantly. CYP3A4 is expressed in all adult human liver and intestine, accounting for more than 50% of total P450 in both organs. Expression is inducible in vivo and in vitro by numerous compounds such as rifampicin, barbiturates and glucocorticoids. In kidney, CYP3A4 is expressed polymorphically. CYP3A4 expression is sex-influenced, as females have 24% greater expression than males. CYP3A5 is detected in 10-30% of Caucasian adult livers, and expressed constitutively in adult kidney. CYP3A5 expression does not appear to be sex-influenced and only moderately inducible by xenobiotics both in vivo and in vitro. CYP3A7 is expressed in fetal liver but only in 25% of adult livers. Molecular mechanisms responsible for the developmentally specific expression of CYP3A""s are unknown.
Since the rates of metabolism of drugs, toxins, etc. can depend on the amounts and kinds of P450s expressed in a tissue, variation in biological response may be determined by the profile of expression of P450s in each person. Analysis of genetic polymorphisms that lead to altered expression and enzyme activity are therefore of interest.
Genetic sequence polymorphisms are identified in the human CYP3A4 gene. Nucleic acids comprising the polymorphic sequences are used in screening assays, and for genotyping individuals. The genotyping information is used to predict the rate of metabolism for CYP3A4 substrates, and the effect that CYP3A4 modulators will have on such metabolism. The information allows better prediction of drug interactions, and effective dose for an individual.
Genbank accession no. S74700 provides the CYP3A5 5xe2x80x2 genomic region. Genbank accession no. D11131 provides a partial sequence of the human cytochrome P450IIIA4 gene. Genbank accession no. M18907 (cDNA) provides the cDNA sequence of a human CYP3A4 allele. Sequences of the CYP3A4 gene are provided in the SEQLIST as follows: cDNA sequence as SEQ ID NO:1, the encoded polypeptide as SEQ ID NO:2, the promoter region as SEQ ID NO:3, intron 3 as SEQ ID NO:4, intron 4 as SEQ ID NO:5, intron 6 as SEQ. ID NO:6, exon 7, intron 7 as SEQ ID NO:7, intron 10as SEQ ID NO:8, intron 11 as SEQ ID NO:9.
Pharmacogenetics is the linkage between an individual""s genotype and that individual""s ability to metabolize or react to a therapeutic agent. Differences in metabolism or target sensitivity can lead to severe toxicity or therapeutic failure by altering the relation between bioactive dose and blood concentration of the drug. Relationships between polymorphisms in metabolic enzymes or drug targets and both response and toxicity can be used to optimize therapeutic dose administration.
Genetic polymorphisms are identified in the human CYP3A4 gene. Nucleic acids comprising the polymorphic sequences are used to screen patients for altered metabolism for CYP3A4 substrates, potential drug-drug interactions, and adverse/side effects, as well as diseases that result from environmental or occupational exposure to toxins. The nucleic acids are used to establish animal, cell culture and in vitro cell-free models for drug metabolism.
It is to be understood that this invention is not limited to the particular methodology, protocols, cell lines, animal species or genera, constructs, and reagents described, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims.
As used herein the singular forms xe2x80x9caxe2x80x9d, xe2x80x9candxe2x80x9d, and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to xe2x80x9ca constructxe2x80x9d includes a plurality of such constructs and reference to xe2x80x9cthe CYP3A4 nucleic acidxe2x80x9d includes reference to one or more nucleic acids and equivalents thereof known to those skilled in the art, and so forth. All technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs unless clearly indicated otherwise.
CYP3A4 Polymorphic Sequences. It has been found that, specific sites in the CYP3A4 gene sequence are polymorphic, i.e. within a population, more than one nucleotide (G, A, T, C) is found at a specific position. Polymorphisms may provide functional differences in the genetic sequence, through changes in the encoded polypeptide, changes in mRNA stability, binding of transcriptional and translation factors to the DNA or RNA, and the like. The polymorphisms are also used as single nucleotide polymorphisms (SNPs) to detect genetic linkage to phenotypic variation in activity and expression of the particular protein.
SNPs are generally biallelic systems, that is, there are two alleles that an individual may have for any particular marker. SNPs, found approximately every kilobase, offer the potential for generating very high density genetic maps, which will be extremely useful for developing haplotyping systems for genes or regions of interest, and because of the nature of SNPs, they may in fact be the polymorphisms associated with the disease phenotypes under study. The low mutation rate of SNPs also makes them excellent markers for studying complex genetic traits.
In order to provide an unambiguous identification of the specific site of a polymorphism, sequences flanking the polymorphic site are shown in the tables, where the 5xe2x80x2 and 3xe2x80x2 flanking sequence is non-polymorphic, and the central position, shown in bold, is variable. It will be understood that there is no special significance to the length of non-polymorphic flanking sequence that is included, except to aid in positioning the polymorphism in the genomic sequence.
The sequence of at least one allele of human CYP3A4 is known in the art, and accessible in public databases, as cited above. This sequence is useful as a reference for the genomic location of the human gene, and for specific coding region sequences. The subject polymorphic sequences are provided in Table 3, and include the CYP3A4-A392/CYP3A4-G392 alternative forms, which are associated with differences in expression level of the polypeptide. As used herein, the term xe2x80x9cCYP3A4 genexe2x80x9d is intended to refer to both the wild-type and variant sequences, unless specifically denoted otherwise.
Nucleic acids of particular interest comprise, the provided variant nucleotide sequence(s). For screening purposes, hybridization probes may be used where both polymorphic forms are present, either in separate reactions, or labeled such that they can be distinguished from each other. Assays may utilize nucleic acids that hybridize to one or more of the described polymorphisms.
The genomic CYP3A4 sequence, including specific transcriptional and translational regulatory sequences, such as promoters, enhancers, etc., including about 1 kb, but possibly more, of flanking genomic DNA at the 5xe2x80x2 end of the transcribed region, is of particular interest. The promoter region is useful for determining the pattern of CYP3A4 expression, e.g. induction and inhibition of expression in various tissues, and for providing promoters that mimic these native patterns of expression. A polymorphic CYP3A4 gene sequence, i.e. including one or more of the provided polymorphisms, is useful for expression studies to determine the effect of promoter and/or intron sequence variations on mRNA expression and stability. The polymorphisms are also used as single nucleotide polymorphisms to detect genetic linkage to phenotypic variation in activity and expression of CYP3A4.
As used herein, the term xe2x80x9cCYP3A4 genexe2x80x9d is intended to generically refer to both the wild-type (reference) and variant forms of the sequence, unless specifically denoted otherwise. As it is commonly used in the art, the term xe2x80x9cgenexe2x80x9d is intended to refer to the genomic region encompassing the 5xe2x80x2 UTR, exons, introns, and the 3xe2x80x2 UTR. Individual segments may be specifically referred to, e.g. exon 2, intron 5, etc. Combinations of such segments that provide for a complete protein may be referred to generically as a protein coding sequence.
The promoter region of CYP3A4 contains a number of sequence motifs for binding transcription regulatory factors. These include a basic transcription element (SEQ ID NO:1, nt. 1054-1071); octamer motif (SEQ ID NO:1, nt. 975-982); TATA box (SEQ ID NO:1, nt. 1075-1081); HNF-5 site (SEQ ID NO:1, nt. 913-920); estrogen responsive elements (SEQ ID NO:1, nt. 735-750, 895-908); CAAT box (SEQ ID NO:1, nt. 843-848); p53 binding site (SEQ ID NO:1, nt. 721-735); AP-3 binding site (SEQ ID NO:1, nt. 682-693); NFSE site (SEQ ID NO:1, nt. 810-819); and progesterone/glucocorticoid responsive element (SEQ ID NO:1, nt.870-883). Regulatory sequences can be used to identify trans acting factors that regulate or mediate CYP3A4 expression.
Fragments of the DNA sequence are obtained by chemically synthesizing oligonucleotides in accordance with conventional methods, by restriction enzyme digestion, by PCR amplification, etc. For the most part, DNA fragments will be of at least 15 nt, usually at least 20 nt, often at least 50 nt. Such small DNA fragments are useful as primers for PCR, hybridization screening, etc. Larger DNA fragments, i.e. greater than 100 nt are useful for production of the encoded polypeptide, promoter motifs, etc. For use in amplification reactions, such as PCR, a pair of primers will be used. The exact composition of primer sequences is not critical to the invention, but for most applications, the primers will hybridize to the subject sequence under stringent conditions, as known in the art.
The CYP3A4 nucleic acid sequences are isolated and obtained in substantial purity, generally as other than an intact mammalian chromosome. Usually, the DNA will be obtained substantially free of other nucleic acid sequences that do not include a CYP3A4 sequence or fragment thereof, generally being at least about 50%, usually at least about 90% pure and are typically xe2x80x9crecombinantxe2x80x9d, i.e. flanked by one or more nucleotides with which it is not normally associated on a naturally occurring chromosome.
CYP3A4 Polypeptides. The CYP3A4 genetic sequence, including polymorphisms, may be employed for synthesis of a complete CYP3A4 protein, or polypeptide fragments thereof, particularly fragments corresponding to functional domains; binding sites; etc.; and including fusions of the subject polypeptides to other proteins or parts thereof. For expression, an expression cassette may be employed, providing for a transcriptional and translational initiation region, which may be inducible or constitutive, where the coding region is operably linked under the transcriptional control of the transcriptional initiation region, and a transcriptional and translational termination region. Various transcriptional initiation regions may be employed that are functional in the expression host. The polypeptides may be expressed in prokaryotes or eukaryotes in accordance with conventional ways, depending upon the purpose for expression. Small peptides can also be synthesized in the laboratory.
Substrate: a chemical entity that is modified by CYP3A4 oxidation, usually under normal physiological conditions. Most of these substrates are lipophilic compounds. Although the duration of drug action tends to be shortened by metabolic transformation, drug metabolism is not xe2x80x9cdetoxificationxe2x80x9d. Frequently the metabolic product has greater biologic activity than the drug itself. In some cases the desirable pharmacologic actions are entirely attributable to metabolites, the administered drugs themselves being inert. Likewise, the toxic side effects of some drugs may be due in whole or in part to metabolic products.
The range of known substrates for CYP3A4 is very broad, including steroids, e.g. testoterone, estradiol, mifepristone; tricyclic antidepressants, e.g. amitriptyline, clomipramine, imipramine, desipramine; SSRI, e.g. citalopram, fluoxetine, fluvoxamine, paroxetine and sertralin; bile acids; protease inhibitors, e.g. saquinovir, indinavir; fatty acids; prostaglandins; leukotrienes; biogenic amines; retinoids; lipid hydroperoxides; phytoalexins; antibiotics, e.g. erythromycin; taxanes, e.g. paclitaxel, docetaxel; anti-hypertensives, e.g. diltiazem; environmental chemicals and pollutants, felodipine, rifabutin, haloperidol, triazolam, terfenadine, lovastatin, chlorzoxazone, alprazolam, etc.
Modifier. A chemical agent that modulates the action of CYP3A4, either through altering its enzymatic activity (enzymatic modifier) or through modulation of expression (expression modifier). In some cases the modifier may also be a substrate, thereby inducing its own demise. Selective inhibitors of CYP3A4 include ketoconazole and troleandomycin. Other P450 selective inhibitors include venlafaxine, clarithromycin, fluconazole, itraconazole, ritonavir, orphenadrine, methimazole, midazolam, gestodene, etc. Recent studies have shown that orally administered grapefruit juice is an expression modifier of CYP3A4, acting to specifically down-regulate expression in enterocytes (Lown et al. (1997) J. Clin. Invest 99:2545-2553).
Recent studies (Schuetz and Schuetz (1996) Mol Pharmacol 49:311-318) on expression of P-glycoprotein and CYP3A4 showed that both proteins were up-regulated after treatment with many drugs, including rifampicin phenobarbital, clotrimazole, reserpine, and isosafrole. P-glycoprotein was up-regulated by midazolam and nifedipine, whereas CYP3A4 was not. Azoles appear to be broad spectrum inhibitors of cytochromes P450.
Pharmacokinetic Parameters. Pharmacokinetic parameters provide fundamental data for designing safe and effective dosage regimens. A drug""s volume of distribution, clearance, and the derived parameter, half-life, are particularly important, as they determine the degree of fluctuation between a maximum and minimum plasma concentration during a dosage interval, the magnitude of steady state concentration and the time to reach steady state plasma concentration upon chronic dosing. The pharmacokinetics of drugs often vary considerably between individuals, largely because of variations in the expression of CYP enzymes in the liver and other tissues. Parameters derived from in vivo drug administration are useful in determining the clinical effect of a particular CYP3A4 genotype.
Expression assay. An assay to determine the effect of a sequence polymorphism on CYP3A4 expression. Expression assays may be performed in cell-free extracts, or by transforming cells with a suitable vector. Alterations in expression may occur in the basal level that is expressed in one or more cell types, or in the effect that an expression modifier has on the ability of the gene to be inhibited or induced. Expression levels of a variant alleles are compared by various methods known in the art. Methods for determining promoter or enhancer strength include quantitation of the expressed natural protein; insertion of the variant control element into a vector with a reporter gene such as xcex2-galactosidase, luciferase, chloramphenicol acetyltransferase, etc. that provides for convenient quantitation; and the like. Specific constructs for determining promoter strength of CYP3A4 are described in Hashimoto et al. (1993) Eur. J. Biochem. 218:585-595.
Gel shift or electrophoretic mobility shift assay provides a simple and rapid method for detecting DNA-binding proteins (Ausubel, F. M. et al. (1989). In: Current Protocols in Molecular Biology, Vol. 2, John Wiley and Sons, New York). This method has been used widely in the study of sequence-specific DNA-binding proteins, such as transcription factors. The assay is based on the observation that complexes of protein and DNA migrate through a nondenaturing polyacrylamide gel more slowly than free DNA fragments or double-stranded oligonucleotides. The gel shift assay is performed by incubating a purified protein, or a complex mixture of proteins (such as nuclear or cell extract preparations), with an end-labeled DNA fragment containing the putative protein binding site. The reaction products are then analyzed on a nondenaturing polyacrylamide gel. The specificity of the DNA-binding protein for the putative binding site is established by competition experiments using DNA fragments or oligonucleotides containing a binding site for the protein of interest, or other unrelated DNA sequences.
CYP3A4 is known to be expressed in liver, e.g. embryonic liver, mature hepatocytes; duodenal tissue, e.g. mucosal epithelial cells; and other epithelial cells throughout the digestive tract; breast tissue; placental tissue; lung tissue, e.g. bronchial glands, bronchiolar columnar and terminal epithelium, type II alveolar epithelium and alveolar macrophages, etc. Hepatic levels of CYP3A4 can be estimated by an erythromycin breath test, and vary by at least 10-fold among patients.
Substrate Screening Assay. Assays to determine the metabolic activity of a CYP3A4 protein or peptide fragment on a substrate. Many suitable assays are known in the art, including the use of primary or cultured cells, e.g. epithelial cells from liver, intestine, etc., genetically modified cells where the native CYP3A4 alleles are altered or inactivated, cell-free systems, e.g. microsomal preparations or recombinantly produced enzymes in a suitable buffer, or in animals, including human clinical trials. Clinical trials may monitor serum, urine, etc. levels of the substrate or its metabolite(s).
Typically a candidate-substrate is input into the assay system, and the oxidation to a metabolite is measured over time. The choice of detection system is determined by the substrate and the specific assay parameters. Assays are conventionally run, and will include negative and positive controls, varying concentrations of substrate and enzyme, etc.
Genotyping: CYP3A4 genotyping is performed by DNA or RNA sequence and/or hybridization analysis of any convenient sample from a patient, e.g. biopsy material, blood sample, scrapings from cheek, etc. A nucleic acid sample from an individual is analyzed for the presence of polymorphisms in CYP3A4, particularly those that affect the activity or expression of CYP3A4. Specific sequences of interest include any polymorphism that leads to changes in basal expression in one or more tissues, to changes in the modulation of CYP3A4 expression by modifiers, or alterations in CYP3A4 substrate specificity and/or activity.
Linkage Analysis: Diagnostic screening may be performed for polymorphisms that are genetically linked to a phenotypic variant in CYP3A4 activity or expression, particularly through the use of microsatellite markers or single nucleotide polymorphisms (SNP). The microsatellite or SNP polymorphism itself may not phenotypically expressed, but is linked to sequences that result in altered activity or expression. Two polymorphic variants may be in linkage disequilibrium, i.e. where alleles show non-random associations between genes even though individual loci are in Hardy-Weinberg equilibrium.
Linkage analysis may be performed alone, or in combination with direct detection of phenotypically evident polymorphisms. The use of microsatellite markers for genotyping is well documented. For examples, see Mansfield et al. (1994) Genomics 24:225-233; and Ziegle et al. (1992) Genomics 14:1026-1031. The use of SNPs for genotyping is illustrated in Golevleva et al. (1996) Am. J. Hum. Genet. 59:570-578; and in Underhill et al. (1996) P.N.A.S. 93:196-200.
Transgenic Animal. The subject nucleic acids can be used to generate genetically modified non-human animals or site specific gene modifications in cell lines. The term xe2x80x9ctransgenicxe2x80x9d is intended to encompass genetically modified animals having a deletion or other knock-out of CYP3A4 gene activity, having an exogenous CYP3A4 gene that is stably transmitted in the host cells; or having an exogenous CYP3A4 promoter operably linked to a reporter gene. Transgenic animals may be made through homologous recombination, where the CYP3A4 locus is altered. Alternatively, a nucleic acid construct is randomly integrated into the genome. Vectors for stable integration include plasmids, retroviruses and other animal viruses, YACs, and the like. Of interest are transgenic mammals, e.g. cows, pigs, goats, horses, etc., and particularly rodents, e.g. rats, mice, etc.
Genetically Modified Cells. Primary or cloned cells and cell lines are modified by the introduction of vectors comprising CYP3A4 gene polymorphisms. The gene may comprise one or more variant sequences, preferably a haplotype of commonly occurring combinations. U.S. Pat. No. 5,429,948, Jul. 4 , 1995 describes the construction and use of a cell line that expresses multiple P450 enzymes.
Vectors useful for introduction of the gene include plasmids and viral vectors, e.g. retroviral-based vectors, adenovirus vectors, etc. that are maintained transiently or stably in mammalian cells. A wide variety of vectors can be employed for transfection and/or integration of the gene into the genome of the cells. Alternatively, micro-injection may be employed, fusion, or the like for introduction of genes into a suitable host cell.
The expression vector will have a transcriptional initiation region oriented to produce functional mRNA, preferably the native transcriptional initiation region, e.g. including the polymorphism described in Table 3. Generally the vectors will include markers for selection, and may also comprise detectable markers operably linked to the CYP3A4 promoter, transcription cassettes for internal controls, etc.
Cell-free Assay Systems. A number of cell-free assays have been described that are useful in the subject invention. Yamazaki et al. (1997) Arch Biochem Biophys 342:329-337 demonstrates reconstituted systems with recombinantly produced CYP3A4. U.S. Pat. No. 5,413,915 describes microsomal P450 oxidase enzyme complex dispersed in a thin film of a generally neutral hydrophilic film-forming binder. Substrates are converted into metabolic intermediates that can be detected by a calorimetric indicator present in the binder film or an adjacent binder film and undergoing a visible color change. U.S. Pat. No. 5,478,723 discloses methods for determining the enzyme or enzymes in the human body that metabolize a particular drug by comparing microsomal fractions from different donors.
The effect of a polymorphism in CYP3A4 gene sequence on the response to a particular substrate or modifier of CYP3A4 is determined by in vitro or in vivo assays. Such assays may include monitoring the metabolism of a substrate during clinical trials to determine the CYP3A4 enzymatic activity, specificity or expression level. Generally, in vitro assays are useful in determining the direct effect of a particular polymorphism, while clinical studies will also detect an enzyme phenotype that is genetically linked to a polymorphism.
The response of an individual to the substrate or modifier can then be predicted by determining the CYP3A4 genotype, with respect to the polymorphism. Where there is a differential distribution of a polymorphism by racial background, guidelines for drug administration can be generally tailored to a particular ethnic group.
The polymorphisms in the sequence of CYP3A4 provided in Table 3, particularly the A to G substitution at xe2x88x92392, are screened for the effect of the polymorphism on expression. Several effects are of interest, including basal expression levels in different tissues, alterations in enzyme activity or specificity, and the induction or inhibition of expression by modifiers. The latter is of particular interest in determining drug-drug interactions. In particular, pharmacokinetic drug interactions with antimicrobials are common because of the tendency to prescribe them in combination with other therapies.
Tissue specific differences in expression are of interest because the metabolism of drugs can vary with the route of administration. For example, certain orally administered drugs are affected by the CYP3A4 expression level in enterocytes, while the same drug administered intravenously is only affected by hepatic expression levels of CYP3A4.
The basal expression level in different tissue may be determined by analysis of tissue samples from individuals typed for the presence or absence, of a specific polymorphism. For example, the CYP3A4 mRNA or protein level in hepatocytes, gastrointestinal epithelial, etc. is determined. Any convenient method may be use, e.g.
ELISA, RIA, etc. for protein quantitation, northern blot or other hybridization analysis, quantitative RT-PCR, etc. for mRNA quantitation. The tissue specific expression is correlated with the genotype.
Alternatively, basal expression levels are determined by expression assays for the particular promoter sequence, as previously described. The assays may be performed with the CYP3A4 coding sequence or with a detectable marker sequence. To determine tissue specificity the assay is performed in cells derived from different sources.
The alteration of CYP3A4 expression in response to a modifier is determined by administering or combining the candidate modifier with an expression system, e.g. animal, cell, in vitro transcription assay, etc. The effect of the modifier on CYP3A4 transcription and/or steady state mRNA levels is determined. As with the basal expression levels, tissue specific interactions are of interest. Correlations are made between the ability of an expression modifier to affect CYP3A4 activity, and the presence of the provided polymorphisms. A panel of different modifiers, cell types, etc. may be screened in order to determine the effect under a number of different conditions.
A CYP3A4 polymorphism that results in altered enzyme activity or specificity is determined by a variety of assays known in the art. The enzyme may be tested for metabolism of a substrate in vitro, for example in defined buffer, or in cell or subcellular lysates, where the ability of a substrate to be oxidized by CYP3A4 under physiologic conditions is determined. Where there are not significant issues of toxicity from the substrate or metabolite(s), in vivo human trials may be utilized, as previously described.
The genotype of an individual is determined with respect to the provided CYP3A4 gene polymorphisms. The genotype is useful for determining the presence of a phenotypically evident polymorphism, and for determining the linkage of a polymorphism to phenotypic change.
A number of methods are available for analyzing nucleic acids for the presence of a specific sequence. Where large amounts of DNA are available, genomic DNA is used directly. Alternatively, the region of interest is cloned into a suitable vector and grown in sufficient quantity for analysis. The nucleic acid may be amplified by conventional techniques, such as the polymerase chain reaction (PCR), to provide sufficient amounts for analysis. The use of the polymerase chain reaction is described in Saiki et al. (1985) Science 239:487, and a review of current techniques may be found in Sambrook et al. Molecular Cloning: A Laboratory Manual, CSH Press 1989, pp.14.2-14.33. Amplification may be used to determine whether a polymorphism is present, by using a primer that is specific for the polymorphism. Alternatively, various methods are known in the art that utilize oligonucleotide ligation as a means of detecting polymorphisms, for examples see Riley et al. (1990) N.A.R. 18:2887-2890; and Delahunty et al. (1996) Am. J. Hum. Genet. 58:1239-1246.
A detectable label may be included in an amplification reaction. Suitable labels include fluorochromes, e.g. fluorescein isothiocyanate (FITC), rhodamine, Texas Red, phycoerythrin, allophycocyanin, 6-carboxyfluorescein (6-FAM), 2xe2x80x2,7xe2x80x2-dimethoxy4xe2x80x2,5xe2x80x2-dichloro-6-carboxyfluorescein (JOE), 6-carboxy-X-rhodamine (ROX), 6-carboxy-2xe2x80x2,4xe2x80x2,7xe2x80x2,4,7-hexachlorofluorescein (HEX), 5-carboxyfluorescein (5-FAM) or N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-6-carboxyrhodamine (TAMRA), radioactive labels, e.g. 32P, 35S, 3H; etc. The label may be a two stage system, where the amplified DNA is conjugated to biotin, haptens, etc. having a high affinity binding partner, e.g. avidin, specific antibodies, etc., where the binding partner is conjugated to a detectable label. The label may be conjugated to one or both of the primers. Alternatively, the pool of nucleotides used in the amplification is labeled, so as to incorporate the label into the amplification product.
The sample nucleic acid, e.g. amplified or cloned fragment, is analyzed by one of a number of methods known in the art. The nucleic acid may be sequenced by dideoxy orothermethods. Hybridization with the variant sequence may also be used to determine its presence, by Southern blots, dot blots, etc. The hybridization pattern of a control and variant sequence to an array of oligonucleotide probes immobilised on a solid support, as described in U.S. Pat. No. 5,445,934, or in WO95/35505, may also be used as a means of detecting the presence of variant sequences. Single strand conformational polymorphism (SSCP) analysis, denaturing gradient gel electrophoresis (DGGE), mismatch cleavage detection, and heteroduplex analysis in gel matrices are used to detect conformational changes created by DNA sequence variation as alterations in electrophoretic mobility. Alternatively, where a polymorphism creates or destroys a recognition site for a restriction endonuclease (restriction fragment length polymorphism, RFLP), the sample is digested with that endonuclease, and the products size fractionated to determine whether the fragment was digested. Fractionation is performed by gel or capillary electrophoresis, particularly acrylamide or agarose gels.
In one embodiment of the invention, an array of oligonucleotides are provided, where discrete positions on the array are complementary to one or more of the provided polymorphic sequences, e.g. oligonucleotides of at least 12 nt, frequently 20 nt, or larger, and including the sequence flanking the polymorphic position. Such an array may comprise a series of oligonucleotides, each of which can specifically hybridize to a different polymorphism. For examples of arrays, see Hacia et al. (1996) Nature Genetics 14:441-447; Lockhart et al. (1996) Nature Biotechnol. 14:1675-1680; and De Risi et al. (1996) Nature Genetics 14:457-460.
The genotype information is used to predict the response of the individual to a particular CYP3A4 substrate or modifier. Where an expression modifier, e.g. a macrolide drug, inhibits CYP3A4 expression, then drugs that are a CYP3A4 substrate will be metabolized more slowly if the modifier is co-administered. Where an expression modifier induces CYP3A4 expression, a co-administered substrate will typically be metabolized more rapidly. Similarly, changes in CYP3A4 activity will affect the metabolism of an administered drug. The pharmacokinetic effect of the interaction Will depend on the metabolite that is produced, e.g. a prodrug is metabolized to an active form, a drug is metabolized to an inactive form, an environmental compound is metabolized to a toxin, etc. Consideration is given to the route of administration, drug-drug interactions, drug dosage, etc.
The CYP3A4-A392/CYP3A4-G392 alternative forms are shown to be differentially distributed between broadly defined racial groups. The G form is more prevalent in African Americans, while the A form is more prevalent in American Caucasians and American Hispanics. The administration of CYP3A4 substrates and expression modifiers may be adjusted to reflect racial differences in metabolism.